Properties of Matter part II Ch. 15

Colloids A colloid (KAH loyd) is a type of mixture with particles that are larger than those in solutions but not heavy enough to settle out. (Example: Milk)

Detecting Colloids A light beam is invisible as it passes through a solution, but can be seen readily as it passes through a colloid. This occurs because the particles in the colloid are large enough to scatter light, but those in the solution are not. This scattering of light by colloidal particles is called the Tyndall effect.

Suspensions Some mixtures are neither solutions nor colloids. One example is muddy pond water. Pond water is a suspension, which is a heterogeneous mixture containing a liquid in which visible particles settle.

Physical Properties Any characteristic of a material that you can observe without changing the identity of the substances that make up the material is a physical property. Examples: color, shape, size, density, melting point, boiling point, ability to flow, mass, volume, length, and magnetism.

Journal for October 6, 2010 List as many physical properties as you can to describe this tennis ball.

The Identity Remains the Same Physical Change The Identity Remains the Same A change in size, shape, or state of matter is called a physical change. These changes might involve energy changes, but the kind of substance—the identity of the element or compound—does not change.

Using Physical Change to Separate Many such areas that lie close to the sea obtain drinking water by using physical properties of water to separate it from the salt. One of these methods, which uses the property of boiling point, is a type of distillation. The process for separating substances in a mixture by evaporating a liquid and recondensing its vapor is distillation.

Chemical Properties and Changes The tendency of a substance to burn, or its flammability, is an example of a chemical property because burning produces new substances during a chemical change. A chemical property is a characteristic of a substance that indicates whether it can undergo a certain chemical change.

The Identity Changes A change of one substance to another is a chemical change. Examples: The foaming of an antacid tablet in a glass of water the smell in the air after a thunderstorm Click image to view movie

The Identity Changes Clues such as heat, cooling, or the formation of bubbles or solids in a liquid are helpful indicators that a reaction is taking place. However, the only sure proof is that a new substance is produced. The only clue that iron has changed into a new substance is the presence of rust. Burning and rusting are chemical changes because new substances form.

Using Chemical Change to Separate One case where you might separate substances using a chemical change is in cleaning tarnished silver. Tarnish is a chemical reaction between silver metal and sulfur compounds in the air which results in silver sulfide. It can be changed back into silver using a chemical reaction.